It is known to employ multistage planetary mechanisms within the rotating housing of heavy duty wheel and track-type vehicle final drives. Usually, two juxtaposed and interconnected simple planetary gear sets or stages have been used to provide the desired speed ratio reduction. However, such simple, two-stage systems are limited to a maximum practical reduction in the speed ratio range of about 50:1. Other final drive mechanisms have employed a planetary gear set with a single group of cluster planet gears; but these mechanisms are more limited in reduction capability than the dual planetary gear sets.
One final drive mechanism offered commercially for use in earthmoving excavators employs three interconnected planetary gear sets of the simple planetary type to provide a reduction in the speed ratio range of about 100:1. It further features an internal parking brake mounted within the supporting spindle, a driving motor mounted in part within the spindle, and a cross connected roller bearing assembly including inner and outer bearing containment races for rotatably supporting the rotating housing structure thereof. While such construction has proven to be very satisfactory, it has too many parts and is more complex than desired. In one embodiment, for example, the first stage has three planet gears, the second stage has four planet gears, and the third stage has five planet gears. Also, the input drive shaft cannot be conveniently removed therefrom for towing of the vehicle. Moreover, the cross connected roller bearing assembly thereof is relatively costly.
Accordingly, what is desired is a simple, rugged and compact multistage planetary final drive mechanism that will provide a speed ratio reduction in the range of about 100:1 or more and that will provide a conveniently serviceable mechanism as well. Specifically, the mechanism should be of a construction sufficient for allowing easy disconnect from the drive motor for towing purposes, and for allowing a simple service check of the planetary gear system inside the housing structure without disturbing more than the outer cover thereof. And, still further, the construction should minimize as much as possible the high costs associated with the use of relatively larger diameter bearing arrangements which desirably permits the motor to be at least partially contained within the supporting spindle for compactness along the transverse central axis thereof.